Currently, most devices designed for carrying information that can be read magneto-optically, such as magneto-optic recording disks, contain a layer of a rare-earth transition metal alloy such as TbFeCo. This material offers adequate performance for current applications at optical wavelengths of 680 nm-830 nm, but is known to suffer drastic decreases at the shorter wavelengths expected in future magneto-optical drives. In particular, the figure of merit (taken to be the reflectivity times the Kerr rotation) and thus the carrier are greatly reduced at wavelengths such as 430 nm. In addition, a higher carrier would be appreciated at the current wavelengths because this would allow for less stringent drive specifications.
Previous attempts to address this problem have been numerous. Frequently, dopants have been added to the rare-earth transition metal alloy. Prominent examples mentioning the two elements described in this patent are Japanese published patent applications J61-240455 and J60-233810.
The formation of Fe/Bi compositionally modulated films was described in Solid State Communications 84, pp 413-415, 1992 (R. Krishnan and H. Lassri). Values for the figure of merit are not explicitly mentioned but can be inferred from the Kerr data to be poor. The material lacks perpendicular anisotropy, therefore measurements of recording performance are impossible. The formation of Co/Bi and Co/Pb superlattices was described in Abstract AC-06 of the 6th Joint MMM-Intermag Conference (1994) (RH. Victora and C.F. Brucker). Again, no perpendicular anisotropy was developed and thus the material could not be tested as a magneto-optical recording medium.
The formation of Fe/Tb multilayers is described in Journal of Applied Physics 59, pp 2514-2520, 1986 (N. Sato) and the formation of Co/Tb multilayers is described in Journal of Applied Physics 69, pp 5989-5991, 1991 (L.-Y. Chen, P. He, S. Nafis, W. A. McGahan, J. A. Woollam, and D. J. Sellmyer). Neither of these materials demonstrate improved figure of merit.
Other uses for these compositionally modulated structures would include magnetic recording media, Faraday isolators, or light modulators.